1) Field of the Invention
A system and method for fabrication of integrated lightning strike protection material are provided. More particularly, a system and method for the fabrication of automated placement of integrated metal resin lightning strike protection material on a composite structure are provided.
2) Description of Related Art
Aircraft and aerospace structures are increasingly being made of composite materials, such as carbon fiber reinforced plastics (CFRP), rather than aluminum alloy and similar metallic materials formerly used, largely because composite materials improve structural performance, provide favorable strength and stiffness characteristics, and reduce aircraft weight. However, composite materials are less conductive than metallic materials and are less capable of withstanding lightning strikes. Composite materials cannot distribute current and heat from a lightning strike, which is typically about 100,000 Amperes at 50,000 Volts, as quickly as metallic materials. Known systems and methods have been developed to provide lightning strike protection for composite structures such as aircraft and aerospace structures. Several known systems and methods add metallic conductors or incorporate metal foil systems of various configurations into composite exterior surfaces of the aircraft, such as skin panels on the wings and fuselage, to provide improved electrical conductivity and distribute and divert current away from flight critical areas and underlying aircraft components, thus minimizing physical damage from lightning strike events. The addition of metallic conductors may include appliqué-based systems that use alternate layers of dielectric and conductive materials applied over the composite structure surface and secured to the surface with an adhesive. This insulates underlying aircraft components from a lightning strike and provides a conductive path for rapid distribution and dissipation of lightning current and heat. The incorporation of metal foil systems may include the use of copper or aluminum foil in either solid or expanded mesh form that is laminated into and co-cured with the composite material. This system provides a conductive path for diversion and distribution of lightning current which, in combination with special fasteners and other features, provides a degree of lightning strike protection for composite structures. However, such known systems and methods often involve manual, tedious, and time consuming placement of multiple material components necessary for effective integration of the lightning strike protection system.
In addition, known systems and methods for lightning strike protection are generally made by individually layering a surfacing top layer to provide a smooth surface for application of subsequent topcoat finish systems, a metal foil layer to conduct lightning current, and an optional isolation layer, typically a resin-reinforced fiberglass ply, to prevent galvanic corrosion and improve thermal expansion mismatches that cause paint and interlaminate cracking. For example, a lightning strike protection material for composite structures is disclosed in U.S. Pat. No. 5,225,265, where the epoxy layer and metal foil layer are not integrated and are individually layered on top of each other. However, the lay-up of these known multilayer systems in separate plies is time consuming and labor intensive. In addition, problems may arise with material wrinkling, contamination, and mishandling of the material. Material tack to tool or composite substrate may also be a challenge when materials are applied individually.
Several material suppliers have offered integrated expanded metal foil and epoxy-based films which minimally improve manufacturing flow time and handling. For example, a known process of making a lightning strike composite is disclosed in U.S. Pat. No. 5,470,413, which provides for a multilayered composite comprising a layer of expanded metal foil, a single layer of epoxy-based resin film, and a carrier layer. Another known system is disclosed in U.S. Pat. No. 7,277,266 for a lightning protection system for a composite structure that is directed to a lightning protection appliqué. However, this known system uses an appliqué that is not co-cured and it uses a pressure-sensitive adhesive. Moreover, these known systems do not allow for automated manufacturing processes to support high volume processing, and in particular, automated handling, cutting, and placement. In addition, known integrated systems may also need additional surfacing layers, such as epoxy surfacing layers, to provide sufficient surfacing, sealing, and smoothness to meet environmental requirements for aerospace applications. While some known systems may be designed to meet environmental requirements, they have not been optimized within the restraints of automatability and minimum weight. Integrated systems designed for lightning strike protection and/or environmental durability have not been created with flexibility and tack requirements. They do not have the tack on both sides so they are unable to go onto contoured surfaces as easily. Moreover, tack on both sides is necessary to stably spool material in automated placement systems. If there are some minorly integrated systems, they have tack only on one side.
Accordingly, there is a need for a system and method for fabrication of integrated lightning strike protection material that does not have the problems associated with known systems and methods.